Execution of the combined three movements puts the foot in an inverted position (inversion) while abduction combined with pronation and plantar flexion puts the foot in an everted position (eversion). Therefore, adduction must be accompanied by supination and slight dorsiflexion. Actually, a movement in one plane must be coupled with displacement in the other two. Įxcept for dorsal and plantar flexions of the ankle joint, the foot moves around the longitudinal axis of the tibia (adduction and abduction), and around its own axis (pronation and supination). Since the trochlea tali is more prominent in the posterior than in the anterior part, the range of extension is greater as compared to the flexion range. By simple subtraction it can be concluded that the total range of dorsal-plantar flexion should be 70–80 degrees. The articular surface of the tibia is a circle sector with the central angle of 70 degrees, with the cusp located on the axis of rotation, while the articular surface of the trochlea tali is a sector with a central angle of 140–150 degrees. The range of dorsal-plantar flexion motions depends mainly on the arc length of articular surfaces. It should be noted that the fork-like structure – formed by the medial and lateral malleoli – shows some elasticity because the tibia and fibula are not connate but held in place by a syndesmosis. In a neutral position or dorsiflexion of the foot, the wider dimension of the trochlea tali is ideally gripped by the fork-like structure of tibial and fibular bony ends. The talus joint is a perfect example of co-operation between the ligament system, muscles and the bony architecture of the joint ends. It not only supports the whole body weight but is also affected by forces resulting from kinetic energy dissipation upon sudden contact with the ground while walking, running or jumping. The joint has closely fitting articular surfaces because it is subject to large loads at the single support stage of the gait cycle. The ankle joint is a synovial hinge joint with only one degree of freedom allowed.
0 Comments
Leave a Reply. |